Sound suppressor



June 8," 1948. w. P. MASON SOUND SUPPRESSOR Filed May 5, 1944 FIG. 5

INVENTOR By W P. MASON n 0 0.1 0.2 as 0.4 0.5 0.0 0.7 0.0 0.9 1.0 ATTORNEY FIG. 6

FREOUENCY- K/LOCYCLES PER SECOND Patented June 8, 1948 SOUND sorrnssson Warren P. Mason, West Orange, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application May 5, 1944, Serial No. 534,259

1 Claim. 1

This invention relates to the transmission of acoustic energy and more particularly to a device for suppressing sound waves in a gas.

The principal object of the invention is to attenuate or suppress sound waves in a gas, especially high pressure waves in a hot gas. Other objects are to reduce the size, weight and cost of silencers or mufllers and to increase the efiective suppression band and the efficiency of such devices.

In designing devices to suppress sound waves of the type associated with the muzzle blast of a firearm or the exhaust of an internal combustion engine ordinary acoustic filter theory is inapplicable because of the high pressure in the wave and the high temperature of the gas. In accordance with the present invention a combination of principles is employed to provide silencers and mufflers which are very efficient in suppressing the sound over a wide frequency range and yet are comparatively simple in construction, low in cost, small in size and light in Weight.

These principles include expanding the gas to reduce the pressure, cooling the gas and dissipating the energy associated with the sound wave before the gas is discharged into the atmosphere. The preferred embodiment of the device comprises'an expansion chamber into which the gas is directed, an exit for the gas and metal screen within the chamber disposed in the path of the gas. In one form the screen may be placed over apertures in transversely disposed metal plates. In another form the transverse members are made entirely of screen and stacked one upon another so as substantially to fill the chamber. When used for firearms the silencer'is attached to the muzzle and, of course, a passageway is provided for the bullet.

The nature of the invention will be more fully understood from the following detailed description and by reference to the accompanying drawings in which like reference characters refer to similar or corresponding parts, and in which:

Fig. 1 is a side view showing a silencer in accordance with the invention in place on a firearm;

Fig. 2 is a side View, partly in section, of the silencer shown in Fig. 1;

Fig. 3 shows one of the plates used in the silencer of Figs. 1 and 2, with the associated layer of screen partly cut away;

Fig. 4 is a side view, partly in section, of a modified form of the silencer shown in Figs. 1 and 2;

Fig. 5 is a cross-section of the silencerof Fig, 4 taken along the line 5-5, with the first two screen sections partly cut away; and

Fig. 6 shows typical attenuation-frequency characteristics obtainable with the silencer of Figs. 1, 2 and 3.

Taking up the figures in more detail, Fig. 1 shows a portion of a firearm l to the muzzle 2 of which is attached a silencer 3 in accordance with the invention. The silencer 3 comprises an expansion chamber H formed by a metallic cylinder 4 and two annular end plates 5 and B. To one of the end plates is secured an internally threaded collar 1 which is screwed onto the externally threaded muzzle 2 to hold the silencer 3 in place.

As shown in Fig 2, within the chamber H are a comparatively large number of closely spaced, transversely disposed metal plates 8 separated by the metallic rings 9. The plates 8 and the rings 9 are welded or otherwise securely attached at their periphery to the cylinder 4. As shown more clearly in Fig. 3, each plate has a circular central hole ID. The holes 10 in the plates 8 andthe holes I2 in the end plates 5 and 6 are linedup with the bore of the fire arm I and preferably are only sufficiently large to permit free passage of the bullet. Each of the plates 8 has a number of apertures l3 covered by a layer of fine metal screen 14 which may be soldered or otherwise secured to the plate 8, preferably on the side facing the muzzle 2. In Fig. 3 a portion of the screen 14 has been removed to show more clearly the plate 8.

Figs, 4 and. 5 show a modified form of the silencer 3 in which the chamber II is substantially filled with annular sections l5 of metal screen stacked one upon another and held under compression by the threaded plug I6 which screws into the internally threaded end of the tube l8. Each of the sections [5 has a central circular hole I! preferably only large enough to permit free passage of the bullet. The sections l5 are preferably made of a metal which is a good conductor of heat such, for example, as copper. In the cross-section of Fig. 5 a part of each of the first two screen sections l5 has been removed'to show a portion of the following section.

As compared with a silencer comprising only non-dissipative branches, the dissipative type of silencer disclosed herein has the advantages that, for a given size, it will provide more attenuation over a wider range of frequencies and, furthermore, it will not accentuate certain frequeneies which may correspond to the natural resoobtainable with the silencer of Figs..1,.2 and,3.

The attenuation in decibels is plotted against the V :15 second. The solid line curve l9 applies to a frequency of the pressure wave in kilocyclesper -10 wave in the chamber I l and dissipates the energy.

Fig. 6 shows typical attenuation characteristics 4 be mounted on the muzzle 2 in a lower position. Although the embodiments of the invention shown are particularly adapted for use as silencers for firearms, it will be recognized that the principles involved are also applicable to other types of sound suppressors such, for example, as mufflers for internal combustion engines. When the device is adapted for use as a mufiler the holes III in the plates 8 and the holes I! in the sections of screen l5 may, in some cases, be made much smaller or entirely eliminated.

What is claimed is A silencer for firearms comprising a cylindrical expansion chamber, means for attaching said silencer having twenty-nine plates 8' spaced 0. 13' of an inch between centers. The plates 8 are two 4. inches in diameter and have central holes onehalf of an inch in diameter. The eight apertures l3 in each plate 8 have a total area of 0.064 of a square inch and are covered by copper screen 14 of 100 mesh per inch made of four mil wire. The broken line curve applies to a silencer which is similar except that the area of the aperture 13 has been reduced by half. It will be noted that the curve 20 shows somewhat less attenuation at frequencies below 0.4 kilocycle but considerably more at the higher frequencies. It is'seen, therefore, that increasing the area of the apertures 13 will improve the attenuation at the low frequencies at the sacrifice of attenuation at the higher frequencies. In addition to the attenuation shown by the curves l9 and 20 of Fig. 6 there will be a reflection loss which may add as much as eight decibels at high frequencies and more at low frequencies. The attenuation may be increased by increasing either the cross-sectional area or the length of the chamber, 7

In the silencer shown in Figs. 4 and 5, the effectiveness in reducing sound is a maximum for sections of screen i5 in the neighborhood of 16 to 20 mesh per inch and decreases if the screen is either finer or coarser. In this type also the attenuation increases with either the length or cross-sectional area of the chamber I I.

In either of the silencers if the diameter of the chamber ll becomes large enough to obstruct the line of sight the passageway for the bullet may be moved toward the top so that the silencer may chamberat one end to the muzzle of a firearm,

a comparatively large number of closely spaced -metal plates'extending transversely across said chamber, and spacing rings positioned between said plates, said plates and said rings being securely attached at their periphery to the walls ofsaid chamber, said plates havingaligned circular holes only sufficiently large to permit free passage of the bullet therethrough, each of said plates having a plurality of comparatively narrow radial slots covered on the side of the plate facing the muzzle of the firearm by fine copper screen of the order of mesh per inch secured to said plate, and the total area of said slots in each of said plates being small compared to the area of the plate.

WARREN P. MASON.

REFERENCES CITED The following references are of record inthe file of this'patent:

H UNITED STATES PATENTS Number 48 9,1 14 Great Britain July 20, 1938 

